INTRODUCTION
Percutaneous iliosacral (IS) screw fixation for pelvic ring injuries is a minimally invasive technique that more effectively reduces blood loss and operative time than the open reduction technique [
1–
3]. Thus, it has several advantages, particularly in patients with unstable hemodynamic conditions. However, the use of one IS screw is inferior with respect to rotational stability and load cycles [
4,
5]. Therefore, the fixation of two unilateral IS S1 screws or the addition of an IS S2 screw is recommended in completely unstable pelvic ring injuries [
4]. Among these two procedures, the fixation of two unilateral IS S1 screws can be a reasonable option for unstable pelvic ring injuries, considering that IS screw positioning in S1 is safer in iatrogenic neurological injuries than IS screw positioning in S2 [
6].
However, limited data have been reported on the clinical outcomes of two unilateral IS S1 screw fixation. Only one study has evaluated the functional and radiological outcomes of two unilateral IS S1 screw fixation and compared them with the outcomes of single IS S1 screw fixation [
7]. Moreover, no other studies have evaluated the clinical outcomes of two unilateral IS S1 screw fixation. Therefore, this study aimed to retrospectively review patients who underwent percutaneous two unilateral IS S1 screw fixation and evaluate their clinical outcomes.
DISCUSSION
The present study demonstrated that percutaneous two unilateral IS S1 screw fixation for pelvic ring injuries required a mean procedure time of 40.1 minutes and led to a mean Hb loss of 0.6 mg/dL during the procedure, a union rate of 100%, and an excellent to good radiological grade of 92.1%.
The biomechanical analysis of IS screws has been performed in several studies. Yinger et al. [
9] compared nine different posterior pelvic ring fixation methods on hard plastic pelvic models, and the results revealed that two unilateral IS S1 screws were significantly stiffer in horizontal plane gapping and coronal plane rotation than single IS S1 screws, two anterior sacroiliac plates, one posterior pelvic tension band plate, one posterior pelvic tension band plate combined with one IS S1 screw, two transiliac bars, two transiliac bars combined with an IS screw, and one transiliac bar with one IS S1 screw. van Zwienen et al. [
4] compared two unilateral IS S1 screws and a single IS S1 screw in a type C pelvic ring injury cadaveric model. The results showed that the two unilateral IS S1 screws were significantly stiffer in terms of rotation and load to failure than a single IS S1 screw. Moreover, Salari et al. [
10] compared two unilateral IS S1 screws and one IS S1 screw with a transsacral S1 screw in a type C pelvic ring injury cadaveric model. They concluded that although a transsacral screw may appear to be more stable, the use of two long unilateral IS SI screws yielded adequate stability in a single-limb stance-testing model compared with transsacral S1 screws. These studies demonstrated the usefulness of two unilateral IS S1 screws with respect to mechanical stability.
Only one study, however, has evaluated the clinical outcomes of two unilateral IS S1 screws to date. The authors compared radiological outcomes via the Matta and Tornetta grade and functional outcomes using the Majeed scoring system. Although the outcomes of both groups were comparable to those of other studies with respect to pelvic ring injuries, the outcomes showed no statistically significant differences between the two groups [
7]. However, they did not report patient-related variables (e.g., age, fracture type, or combined injury) of each group and their differences. Therefore, selection bias could not be excluded with regard to the results of the previous study [
7]. Suda et al. [
5] recently evaluated the safety of two unilateral IS S1 screws in a three-dimensional dataset of 1,000 hemi-pelvises of 500 patients with trauma. They concluded that 99% of male and 96% of female hemi-pelvises had adequate room to place two 7.3-mm screws at a 5-mm distance into the S1 vertebra. In addition, they stated that two unilateral IS S1 screws increased the mechanical stability and posed a lower risk for neurological injuries than the positioning of additional S2 screws.
In the present study, the mean procedure time of percutaneous two unilateral IS S1 screw fixation was 40.1 minutes, which is comparable to the procedure time in previous studies that used a single IS screw. Routt et al. [
11] reported that one percutaneous IS screw required a mean procedure time of 26 minutes, implying that 2-screw fixation would require a mean time of 52 minutes. Gras et al. [
12] reported a mean time of 62 minutes for one percutaneous screw fixation for pelvic ring injury. Although positioning the second IS S1 screw to avoid the first IS S1 screw can be intuitively difficult and may need a longer time, it did not require more time in the present study. Thus, two unilateral IS S1 screws still have the advantage of a short procedure time for performing the percutaneous IS screw technique. We evaluated blood loss by measuring the decrease in Hb levels between the preoperative and postoperative periods, although most other studies utilized intraoperative blood loss volume. Because intraoperative blood loss volume cannot be evaluated objectively and is often estimated, we used Hb loss instead. The mean Hb loss of 0.6 g/dL was small, which is beneficial for hemodynamically unstable patients. Moreover, all patients showed bone union, and bone union required a mean duration of 153.2 days. These results are comparable to those of other studies that used percutaneous IS screws or open reduction and plate fixation [
12–
14]. The results of the Matta and Tornetta grades were also comparable to or better than those of other studies. Matta and Tornetta et al. [
8] reported an excellent grade in 67% of patients, good in 28%, fair in 4%, and poor in 1%. In addition, Suzuki et al. [
15] reported an excellent grade in 51% of patients, good in 23%, fair in 16%, and poor in 10%. Furthermore, Khaled et al. [
7] reported an excellent grade in 71.4% of patients, good in 20.8%, fair in 7.8%, and poor in none. There were no intraoperative complications; however, eight patients developed postoperative complications. In particular, S1 screw loosening (2.6%), widening of the symphysis pubis (5.3%), lumbosacral plexopathy (2.6%), and S1 radiculopathy (2.6%) were directly related to two unilateral IS S1 screws. Moreover, all neurological deficits recovered spontaneously; the 2.3- and 2.5-mm widenings of the symphysis pubis after surgery were relatively smaller than the mean values in previous studies [
16–
19]. The results for complications are also comparable to the findings of a study on a single IS screw; Osterhoff et al. [
1] performed percutaneous single IS screw fixation on the S1 or S2 vertebrae in 38 patients and reported persistent hypoesthesia in L5/S1 dermatomes in two patients (5.3%); screw malpositioning or loosening, which needed secondary surgery, in four (10.5%); pulmonary embolism in one (2.6%); and nonunion in one (2.6%). Zwingmann et al. [
20] evaluated the intraoperative and postoperative complications of the CT guidance and conventional technique groups for percutaneous IS screws in 784 patients and reported intraoperative and postoperative complications in 8.8% and 26.3% of patients in the CT guidance group and 5.9% and 29.3% of patients in the conventional technique group, respectively. Therefore, in this study, percutaneous two unilateral IS S1 screw fixation required a short procedure time and showed a small amount of blood loss, 100% bone union rate, comparatively good radiological outcomes, and few complications.
The limitations of this study are the retrospective study design and small number of cases, particularly for the outcome of Hb loss. In addition, this study was a case series and did not include a control group. Moreover, the outcomes of this study included many variables that were not controlled, including the initial fracture type or the fixation construct of the anterior pelvic ring. Thus, an additional study with a large number of cases and high power is needed.
In conclusions, percutaneous two unilateral IS S1 screw fixation is a useful option for pelvic ring injuries. In particular, the procedure requires less time and causes little blood loss, as well as leading to a 100% bone union rate and good radiological outcomes.